In a fuel cell system using hydrogen as a fuel gas, a hydrogen gas tank, a liquid hydrogen tank, a tank filled with a hydrogen storage material, or the like is used as a hydrogen source. In those tanks, a tank filled with a hydrogen storage material has a high hydrogen storage density per unit volume and hence can contribute to the downsizing of a system. Consequently, a fuel cell system using the tank is appropriate in particular as an energy source of a movable body.
Since a fuel cell has an appropriate operating temperature range, the temperature of the fuel cell has to be maintained in an appropriate temperature range in order to obtain high power generation efficiency. Further, since a hydrogen storage material generates heat when a hydrogen gas is absorbed and absorbs heat when a hydrogen gas is desorbed, the heat management of the hydrogen storage material is required in order to absorb and desorb hydrogen on a timely basis.
Now, various proposals have heretofore been given in order to solve the problems.
Patent Literature 1, for example, discloses a fuel cell system of, when the fuel cell system starts,
(a) supplying electric power to a drive motor in the state of fixing a vehicle drive output shaft of the drive motor, discharging the electric power consumed by the drive motor as heat, and raising the cooling water temperature of a fuel cell by using the heat, and at the same time(b) making a fuel cell stack generate electricity at an output power lower than electric power that can be generated, making the fuel cell stack itself generate heat, and thus warming up the fuel cell stack from the interior.
The literature describes that the warm-up of a fuel cell stack can be accelerated by such a method without increasing an energy loss.
Further, Patent Literature 2 discloses a cooling system controller of, when a coolant of a fuel cell and another heat dissipation unit are cooled simultaneously by using a radiator fan, splitting the coolant of the fuel cell in a radiator direction and in a radiator by-pass direction at predetermined ratios.
The literature describes that the temperature of the coolant of a fuel cell can be restrained from being lowered excessively by feeding the coolant of the fuel cell more in the radiator by-pass direction when another heat dissipation unit is mainly cooled by using a radiator fan.
Furthermore, Patent Literature 3 discloses a cooling controller for a fuel cell of, when a coolant is circulated between a fuel cell and a radiator and the radiator is cooled with a fan,
(a) setting a restricted rotation number for the rotation number of line fan,
(b) making the restricted rotation number variable in response to the usage environment of the fuel cell, and
(c) changing the restricted rotation number in the manner of delaying from the variation of the usage environment when the usage environment of the fuel cell varies and the restricted rotation number is required to change.
The literature describes that the requirements of both cooling performance and sound vibration performance can withstand by such a method.
In addition, Non-patent Literature 1 proposes a system of installing two reactor vessels containing a hydrogen storage alloy between a hydrogen tank and a fuel cell, and using heat generation and heat absorption accompanying the absorption and desorption of hydrogen in the hydrogen storage alloy for air conditioning.
The temperature management of a fuel cell is generally carried out with a radiator. In the case of circulating a coolant between a fuel cell and a radiator, a temperature difference ΔT between the temperature of the heat exchange part of the radiator and an ambient temperature is low when the exhaust heat temperature of the fuel cell is relatively low. On this occasion, a large-sized radiator is required in order to dissipate the heat from the fuel cell efficiently. When a large-sized radiator is used, however, the degree of freedom in the shape of a fuel cell system lowers.
Meanwhile, Non-patent Literature 1 discloses a system of using heat generation and heat absorption accompanying the absorption and desorption of hydrogen in a hydrogen storage alloy for air conditioning. For example, when cooling is required in air conditioning, however, hydrogen can be desorbed from a hydrogen storage alloy by using the heat of the air conditioning, but the heat generation during hydrogen absorption cannot be used for the air conditioning. When heating is required in air conditioning in contrast, the heat generation during hydrogen absorption can be used for air conditioning, but another heat source is required when hydrogen is desorbed from a hydrogen storage alloy. Consequently, the effective utilization of heat is insufficient merely by a system of thermally connecting a hydrogen storage alloy and air conditioning.